PHP extension pass an object as parameter

Hello

i trie to port the PEAR HTML_Template_Sigma Class to an PHP extension.

in the PHP Class are some callback functions registert

$this->setCallbackFunction('e', array(&$this, '_htmlentities'));
$this->setCallbackFunction('u', 'urlencode');

the easier callback's to a php function i managed with this code


 zval tplFunction;
 ZVAL_STRING(&tplFunction,"u");
 zval callback;
 ZVAL_STRING(&callback,"urlencode");

 zend_call_method_with_2_params ( obj,Template_Sigma, NULL,
"setcallbackfunction", NULL, &tplFunction, &callback);


but how can i pass the object from a private method of the PHP extension
class to the  setcallbackfunction as it is down in PHP with

array(&$this, '_htmlentities')


Best Regards Torsten